Robot joints used in robotic arms are well known. However, when joints and arms are to be used in certain applications constraints are introduced in the specifications that are not generally present in general applications. For example the payload to weight ratio is very important in space and planetary applications and mobile robot applications. As well, size constraints may be very important in manufacturing and mobile robot applications. Any design of modern robot needs to consider: low weight, high payload, long reach, kinematic dexterity, high accuracy and repeatability, and low cost.
Accordingly most of the above considerations can be addressed by the combination of two joints in a single module which would be advantageous over separate first joint and second joints. A combination two joint module may provide advantages in regard to a compact size, low weight, high payload, and high accuracy and repeatability. Such joints are particularly useful in robotic arms. As well, modular robotic arms having internal cables are advantageous over conventional robotic arms.